GB2117867A

GB2117867A - Pneumatic flexible-walled spring

Info

Publication number: GB2117867A
Application number: GB08308768A
Authority: GB
Inventors: Achille Galliza
Original assignee: Industrie Pirelli SpA; Pirelli SpA
Current assignee: Industrie Pirelli SpA; Pirelli and C SpA
Priority date: 1982-04-01
Filing date: 1983-03-30
Publication date: 1983-10-19
Also published as: GB8308768D0; GB2117867B; IT8220536A1; IT8220536A0; FR2524593A1; IT1150509B; DE3311853A1

Abstract

A generally cylindrical open- ended membrane 1 is secured at each of its ends to a closure means 4. The membrane is internally reinforced by wires (2) extending parallel to one another according to the generatrices of the cylindrical shape. The membrane has an undulating wall and is supported externally by rigid bodies which may be (a) the coils of a wire helix 3 or (b) axially spaced rings. The wall undulations match the wire helix or the spaced rings, and the helix pitch/ring spacing need not be uniform. The closure means comprises a plate and a ring fastened together to clamp between them the membrane end which has been turned-up around the end convolution of the helix or the respective ring. <IMAGE>

Description

SPECIFICATION Pneumatic spring The present invention relates to a pneumatic spring, namely, to a device comprising a flexible envelope in the form of a membrane tightly connected to two rigid (for example, metallic) bodies and a fluid (in particular, air) under pressure in the membrane.

Many types of pneumatic springs are known; in particular, these types may all be said to be, in essence, a pneumatic spring which is constituted by an envelope, formed by a membrane of elastomeric material in which is incorporated a resistant structure formed by rubberized plies of textile or metallic wires with the wires of the different plies being crossed with respect to one another, said structure being open at its two ends.

Said envelope is releasably connected, at said open ends, in a fluid-tight manner to rigid (preferably metallic) bodies by means of which the envelope is closed and which form part of the means for connection of the spring to the machine or the like to which the spring must be fitted. In the present description, the word "textile" as applied to wires has the meaning conventionally attributed to it in the tyre industry and comprises, by way of example, organic textile materials (for example, cotton and rayon) and fibres from synthetic polymers (for example, polyamide fibres and polyester fibres).

The known pneumatic springs, whose principal features are summarised in the preceding paragraph, have different drawbacks:- (a) A first drawback resides in the low pressure with or at which said springs must work. Said pressure does not exceed the value of from 8 to 9 Kg/cm2 and leads to the big transverse dimensions of said springs and also rules them out for machines and the like which are subjected to heavy conditions of use.

(b) A second drawback resides in the fact that their working life results in an unsatisfactory (i.e.

too short) lifetime of the flexible envelope which constitutes one of the essential elements of the spring.

(c) A third drawback is traceable to the necessity of effecting very precise workings on the zone in which the flexible envelope is tightly joined to the rigid bodies; this causes high manufacturing costs and a non-security (always present) to the effects of the tightness in the said zones of connection between the envelope and said bodies.

The present invention aims at trying to overcome all of the drawbacks mentioned above in order to increase the permissible loads on the springs, in order to reduce the transverse dimension, in order to extend their useful working life and in order to permit the springs to have a large range of response characteristics to the loads applied to them.

Accordingly, the present invention consists in a pneumatic spring which comprises a substantially cylindrical membrane of elastomeric material embedding a resistant structure formed by a plurality of flexible and inextensible wires arranged according to the generatrices of the cylindrical shape and a plurality of rigid annular bodies spaced from one another, coaxial with the membrane and arranged therearound being provided, said rigid annular bodies being in contact with the outer surface of said membrane and the edges of this latter being connected to the rigid annular bodies spaced from one another.

Some embodiments of a pneumatic spring according to the present invention will now be described, by way of example only, with reference to the accompanying drawing, in which: Figure 1 shows in perspective view a pneumatic spring according to the invention; and Figure 2 shows a detail view, drawn to an enlarged scale and in section, of one particular of the spring of Figure 1.

In its more general aspect, a pneumatic spring according to the invention comprises an envelope open at its two ends and formed by a substantially cylindrical membrane of elastomeric or other suitable material in which is incorporated a plurality of flexible and inextensible wires which are arranged substantially according to the generatrices of the cylindrical shape, a plurality of rigid annular bodies being in contact with the outer surface of the membrane and acting as rings of said membrane.

Moreover, the rigid annular bodies farther from one another are connected to the membrane forming the envelope by virtue of the fact that the ends of said membrane are turned-up around said annular bodies and connected to the outer surface of the membrane itself. In this way, in the more general aspects of a pneumatic spring according to the present invention, each of the ends of the membrane connected to the rigid annular bodies farther from one another constitute a sealing ring which is encased between a pair of flanges so as to permit to these latter to form a rigid body associated to the membrane.

As shown in Figures 1 and 2, the pneumatic spring comprises an envelope 1 of elastomeric material and open at its two ends. A resistant structure formed by a plurality of wires 2 is embedded in said material. A so-called ring 3 extends around the outer surface of the envelope 1 and rigid bodies 4 close the open ends of the envelope 1. The wires 2 are parallel, or nearly so, to one another and not in contact with one another.

The envelope 1 is of generally cylindrical shape but is provided with an undulation which is such so as to create a plurality of convex crests 5 separated from one another by concave troughs 6.

Said crests 5 have a helical path, as also do the troughs 5, the troughs serving to accommodate the convolutions of a wire helicoid 7 of high resistance, namely, a real wire mechanical spring.

The individual convolutions of the helicoid 7 are kept in the troughs 6 by a strip 8 whose centrai part is in contact with said convolutions and whose edge portions are connected (for example, by an adhesive) to the outer surface of the envelope 1.

The wires 2, which are of flexible and inextensible material (such, for example, as glass fibres, nylon and steel) are substantially arranged according to the generatrices of the cylindrical shape of the envelope 1.

The envelope 1 has its own ends connected to the respective end turns 7' of the wire helicoid 7.

Each end of the envelope 1 is turned-up around the respective end turn 7' so that the free end portion 9 of the envelope 1 forms a pocket 10 in which said turn 7' is encased, the edge portion being connected (for example, through an adhesive) to the outer surface of the envelope.

Disposed within the envelope in the region of the end turn 7' is an annulus 12 of which a radially outer portion 1 3 is bent out of the plane of the remainder thereof, as seen in Figure 2. Outside the envelope in the region of the end turn 7' is a circular plate 11 of which a radially outer portion 14 is bent out of the plane of the remainder thereof: the plate 11 is therefore slightly dished.

Both the plate 11 and the annulus 12 are provided with threaded through holes 1 5 which are brought into alignment and have threaded bolts 1 6 screwed in order to effect a releasable connection between them and also, simultaneously, tightening up against the turn 7' and, in so doing, clamping the pocket 10 between said turn and the plate 1 1/annulus 12.

As shown in Figures 1 and 2, the rigid wire helicoid 7 has a constant pitch and the convolutions thereof are connected to the envelope 1 which is ringed by said convolutions.

However, these two features are not to be considered as limiting because said pitch of the turns can be varied to obtain the desired characteristics (rate) of the pneumatic spring, and said turns need not be firmly connected to the outer surface of the envelope 1.

In an alternative embodiment which is not illustrated, in place of the rigid wire helicoid 7 there is provided a plurality of rigid annular bodies (rings) which can be either firmly connected to the surface of the envelope 1 (for example by being covered by strips 8 similar to those in Figure 2) or simply in annular troughs which are provided in the envelope 1 and which are similar to the troughs 6 mutatis mutandis.

Lastly, associated with the plates 11 , there are provided means (not shown) to convey and to keep a fluid, for example air, under pressure within the envelope 1.

By providing a reinforcing structure for the envelope 1, said structure being formed by flexible and inextensible wires arranged according to the generatrices of the substantially cylindrical shape of said envelope 1, small bending radii for said wires are obtained in any load condition of the spring.Since the resistance to stresses by the envelope 1 depends on the resistance to stresses of the wires forming the resistant structure and since (by reducing the bending radius which the wires can assume) the resistance to stresses of said wires and consequently of the envelope 1 increases proportionally; this has meant that the envelope is able to withstand greatly higher pressures than those which have been withstood by the envelopes of the known air springs which, having resistant structures made by plies of crossed wires oblige these plies to assume large bending radii in order to cope with working pressures of about 1 5-1 6 Kg/cm2.

Moreover, as far as concerns the generally preferred and illustrated embodiment, the rigid wire helix (itself constituting a mechanical spring) around the outer surface of the envelope 1 of the pneumatic spring, is able to bear alone a part of the outer load acting on the pneumatic spring according to the present invention and therefore for this reason also a pneumatic spring according to the present invention is able to bear higher loads than those which it would be able to if only the envelope 1 were present.

As to the reaching of a longer useful lifetime for a pneumatic spring according to the present invention than the service lives of the previously discussed known types, it is thought but not warranted that the explanation derives from the fact that the resistant structure of the envelope 1 being formed by a plurality of wires which are parallel or substantially parallel to one another and consequently not in mutual contact, slidings among the wires cannot occur; this turns into a great resistance to the fatigue stresses of the envelope and therefore to its longer service life which produces a longer life of the pneumatic spring incorporating said envelope.

Lastly, the connection between the envelope 1 and the rigid bodies at its opposite ends that together originate a pneumatic spring does not require workings of high accuracy and, hence, high cost. In fact from the description of Figure 2, it will have been realised that the turning-up of each of the ends of the envelope 1 around the respective end turn of the wire helix leads to the creation of a kind of fluid-tight seal which, having to work clamped between two elements (plate 1 1/annulus 12) which together constitute a rigid body, does not require for itself and for said elements a working accuracy to guarantee the fluid-tightness. By means of the connection between the envelope 1 and said elements, it is not necessary, at the limit, as indicated in the particular embodiment shown in and described with reference to Figures 1 and 2, to effect the connection of the free edge portion of the envelope 1 against the outer surface thereof because the clamping of the turned-up end of the envelope between the end turn 7' and the plate 1 1/annulus 12 provides all of the necessary security, and this in turn produces a great constructive simplification of the pneumatic spring. Moreover, this connection between envelope 1 and said elements has great strength and guarantees optimum fluid-tightness of the envelope in any working condition of the pneumatic spring.

Claims

1. Pneumatic spring comprising a substantially cylindrical membrane of elastomeric material in which is incorporated a resistant structure formed by flexible and inextensible wires which are arranged according to the generatrices of the cylindrical shape; a plurality of first rigid bodies axially spaced from one another along the membrane, said bodies being coaxial with the membrane and arranged therearound in contact with the outer surface of said membrane; and the ends of said membrane being connected to other rigid elements.

2. Pneumatic spring according to Claim 1, wherein the first rigid bodies are the convolutions of a rigid wire helicoid.

3. Pneumatic spring according to Claim 1 or Claim 2, wherein the convolutions of the rigid wire helicoid are connected to the outer surface of the membrane.

4. Pneumatic spring according to Claim 2 or Claim 3, wherein the substantially cylindrical membrane has an undulating wall such that the convolutions of the helicoid are accommodate in the concave troughs of the undulations and are separated from one another by convex crests of said undulations.

5. Pneumatic spring according to any one of Claims 2 to 4, wherein the pitch of the convolutions of said helicoid is not uniform.

6. Pneumatic spring according to Claim 1, wherein the first rigid bodies are annuli.

7. Pneumatic spring according to Claim 6, wherein the spacing of said annuli from one another is not uniform.

8. Pneumatic spring according to Claim 6 or Claim 7, wherein each of the annuli is accommodated in a concave trough of the undulating wall of the membrane, the concave troughs being separated from one another axially of the membrane by convex crests.

9. Pneumatic spring according to any one of the preceding Claims, wherein the ends of the membrane are turned-up around the respective first rigid bodies.

10. Pneumatic spring as claimed in Claim 9, wherein said other rigid elements consist, for each end of the membrane, of a plate and an annulus which are releasably secured to one another in such a manner as to clamp the respective end of said membrane between themselves and said respective first rigid bodies.

11. Pneumatic spring constructed, arranged and adapted to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.

1 2. Any features of novelty, taken singly or in combination, of the embodiments of the invention hereinbefore described with reference to the accompanying drawing.